The present invention relates to a musical tone control signal generating apparatus for an electronic musical instrument and, more particularly, to a musical tone control signal generating apparatus which can generate a musical tone control signal having a level corresponding to an operation position when a performer operates a musical tone control operation element.
In some musical tone control signal generating apparatuses of this type, a musical tone control signal is generated so as to provide a so-called pitch-bend effect to a musical tone using an automatic return type musical tone control operation element (U.S. Pat. No. 4,347,772).
For example, in a hand-held performance type electronic musical instrument 1 shown in FIG. 15, a keyboard unit 3 is arranged on a front surface portion of body portion 2 to extend in the right-and-left direction. A pitch-bend operation element 5 serving as a musical tone control operation element is arranged on a rear surface portion of a distal end portion of a neck portion 4 which projects to the left from the left end portion of the body portion 2. In a hand-held state in which a strap 6 attached to the body portion 2 is put on a performer's shoulder, he depresses a key at the keyboard unit 3 with a finger or thumb of his right hand, and pivots the pitch-bend operation element 5 from the rear surface side with the first, second, or third finger of his left hand while holding the neck portion with his left hand, thereby changing the pitch of the musical tone corresponding to the depressed key in accordance with a pivot position of the pitch-bend operation element 5.
The pitch-bend operation element 5 has the following structure. As shown in FIGS. 15 and 2, a wheel 11 partially projects from a panel surface of the neck portion 4. The performer rubs his finger on anti-slip notches 12 formed on the periphery of the wheel 11 to reciprocally pivot the wheel 11.
The pivot shaft of the wheel 11 is coupled to a pitch-bend volume 28 comprising a variable resistor, and a recess 13 is formed on the outer surface of the wheel 11. The recess 13 can be pivoted from a minimum operation position MIN toward a maximum operation position MAX, as indicated by an arrow a (called a forward operation), and can be pivoted from the maximum position MAX toward the minimum position MIN, as indicated by arrow b (called a reverse operation).
A return spring 11a is attached to the wheel 11. When the performer releases his finger from the wheel 11, the wheel 11 is automatically returned to a predetermined operation position by the return spring 11a (this automatic return position will be referred to as a middle operation position hereinafter).
The performer can easily confirm the automatic return operation of the wheel 11 since the recess 13 is returned to the predetermined middle operation position MID corresponding to the middle point between the maximum and minimum positions MAX and MIN.
When the pitch-bend effect is no longer required to be provided to a musical tone, the performer releases his finger from the pitch-bend operation element 5 so as to cause the wheel 11 to return to the middle operation position MID. Thus, a performance state for generating a musical tone with the pitch-bend effect can be immediately switched to a performance state without the pitch-bend effect. As a result, the pitch-bend effect can be provided as easy as possible.
However, when the pitch-bend operation element with the above arrangement is used, if the performer releases his finger from the wheel 11 while he pivots the wheel 11 to the position other than the middle operation position MID, the wheel 11 cannot often be accurately returned to the middle operation position MID.
The return spring for returning the wheel 11 to the middle operation position MID and a mechanical pivot mechanism portion of the wheel 11 inevitably fatigue as the pitch-bend operation element 5 is repeatedly used. For this reason, the wheel 11 cannot be correctly returned to the middle operation position MID.
In this state, the pitch of a key depressed at the keyboard unit 3 is offset higher or lower by an offset of the return position of the wheel 11 from the correct middle operation position MID.
When an electronic musical instrument is driven by a battery, if a power supply voltage varies, in particular, if a voltage is decreased and the operation element is located at a predetermined middle position, a signal derived from a variable resistor cooperating with the operation element cannot often have a correct signal level. In this case, if the operation element is used for pitch-bend, a pitch is offset higher or lower even if the element is located at the correct middle position.